Removal-proof magnet system for electric machines



May 29, 1962 F. WINTER 3,037,134

- REMovAL- RooF MAGNET SYSTEM FOR ELECTRIC MACHINES Filed June 1, 1960 713 6 F/G.l

Ml/am fiwvz w INTER United States Patent 3,037,134 REMOVAL-PROOF MAGNET SYSTEM FOR ELECTRIC MACHINES Franz Winter, Linz (Danube), Austria, assignor to Elektro-Bau A.G., Linz (Danube), Austria Filed June 1, 1960, Ser. No. 33,289 Claims priority, application Austria Oct. 9, 1959 4 Claims. (Cl. 310-153) The magnet system of pole wheels having poles consisting of permanent magnets has the advantage that the ampere turns required for excitation must be provided only once-during the magnetizing process-so that a separate exciter winding, which involves structural expenditure and power consumption, is not required. On the other hand, the magnetic energy impressed upon the magnet by the magnetizing process and effective during operation depends on the resistance or counter-ampere turns present in the magnetic circuit in accordance with the demagnetizing curve of the magnetic material so that an increase of the magnetic resistance in the magnetic circuit, as will take place when such a pole wheel is subsequently removed from the stator, will result in a deterioration of the magnetic operating properties.

In order to maintain the magnetic properties of the magnetic material within a specific magnetic operating circuit it is, therefore, necessary to remagnetize the magnet system when the pole wheel has been removed, e.g., during repairs. This remagnetizing requires special apparatus which, in most cases, is not available in repair shops. For this reason the magnet system mainly of smaller machines has been so amply dimensioned that the magnetic energy which remains after the removal provides values which are suificient for the operating. condition. This design, however, is economically intolerable for larger magnet system because of the low utilization of the magnetic material.

For this reason devices have already been disclosed which are intended to prevent a weakening of the magnets when they are removed from and reincorporated in the magnetic operating circuit.

In a known construction this is effected by sleeves which consist of soft magnetic material and enclose the several magnets and are suitably used during the magnetizing process. In another known construction, separate magnetic short circuiting rings are provided, which establish magnetic short circuits between the pole pieces of the several permanent magnets in the completely magnetized pole wheel and which are removed when the pole wheel has been incorporated.

As such means which prevent a demagnetization may not always be available or may be overlooked when a removal is desired, such suggestions for protecting the magnetic system during disassembly cannot be fully satisfactory and their use is mainly restricted to the manufacture in the manufacturing plant. Special methods must be adopted to enable a foolproof removal of the magnet system and satisfactory repairs particularly of seriesmanufactures products even in modestly equipped workshops.

For this purpose it is already known to provide a separate magnetic short-circuiting circuit outside the pole wheel in addition to the elements of construction required for operation. This is possible in the case of smaller machines without special economic disadvantages.

In larger electric machines, particularly in machines comprising revolving external poles, which are provided on an increasing scale with permanent magnet systems, however, the present invention affords considerable advantages in that the magnetic short-circuiting circuit consists of an existing part of construction, namely, the fan wheel which rotates with the pole wheel and the air guide ribs of which serve as magnetic short-circuiting yokes for the several permanent magnets when the magnet system has been removed.

The invention will be described more fully with reference to an illustrative embodiment consisting of a medium frequency generator comprising numerous permanent poles. FIG. 1 of the accompanying drawing shows the operating condition whereas FIG. 1b shows the condition in which the permanent magnet system is shortcircuited.

The present case applies to a machine of the external pole-type, comprising magnet poles 1 and a magnet ring 2, which are driven by means of the supporting shaft 3. The stator 4 with the winding 5 is stationary and has appropriate ball bearings 6 for mounting the shaft 3.

The magnet wheel or rotor 1, 2 is firmly secured to the fan wheel 7 by screws 8 so that it has a bell-shaped appearance. The hub 9 of this bell is firmly secured to the driving shaft 3 in a manner known per se. Any attempt to remove this bell and with it the magnet system, e.g., for a replacement of bearings or for re-winding, is prevented by a locking means consisting in the present case of a pin 10, which extends through a hole in the hub 9 and into a bore in the shaft 3. This pin cannot be urged by the force of the spring 11 out of the bore in the shaft 3 to rele'ase the lock and enable the withdrawal of the bell consisting of the fan wheel 7 and the magnet ring 1, 2 until the screws 8 have been loosened and the magnet ring 1, 2 has been sufficiently displaced in the direction of the stationary fan wheel 7 to enable the pin 10 to slide into an aperture 12 of the magnet ring 2 (FIG. 1b) because an internal wall of the magnet ring 2 normally blocks outward movement of the pin 10. By the displacement of the magnet ring the several magnets have been removed to positions over the ribs 13 of the fan wheel and have thus been magnetically short-circuited.

The entire bell 1, 2, 7 can now be withdrawn as a whole from the shaft 3 without endangering the magnet system so that the internal parts of the machine become accessible for repairs.

For re-fitting the bell, the hub 9 is pushed on and secured to the shaft 3 and the pin is forced against the force of the spring 11 into the hole of the shaft 3, whereafter the magnet ring 1, 2 is laterally displaced to its original position (FIG. la) over the stator 4 and is then again firmly connected to the fan wheels 7 by the screws 8.

What is claimed is:

1. In an electromagnetic machine, in combination,

(a) a supporting member having an axis;

(b) a rotor member rotatable about said axis;

(0) fan wheel means of magnetizable material;

(d) a plurality of permanent magnet means on one of said members, said one member being axially movable relative to said fan wheel means between a first position in which said fan wheel means constitutes a magnetic flux path between said plurality of magnet means, and a second position spaced from said first position; and

(e) locking means on said fan wheel means alternatively engageable with said members for securing said fan wheel means against axial movement relative to the respective member.

2. In a machine as set forth in claim 1,

(f) resilient means permanently urging said locking means into engagement with said one member; and

(g) blocking means on said one member for preventing engagement of said locking means with said one member \when the latter is spaced from said first position thereof.

3. In an electromagnetic machine, in combination,

(a) a supporting member having an axis;

(b) a rotor member rotatable about said axis;

(0) rfan wheel means of magnetizable material;

(d) releasable fastening means for securing said fan wheel means to said rotor member for rotation therewith about said axis.

(e) a plurality of permanent magnet means on said rotor, said rotor member being axi-ally movable relative to said fan wheel means between a first position in which said fan wheel means constitutes a magnetic flux path between said plurality of magnet means, and a second position spaced from said first position when said fastening means is released;

(1) locking means on said fan wheel means alternatively engageable with said member for securing said fan wheel means against axial movement relative to the respective member;

(g) resilient means permanently urging said locking means into engagement with said rotor member; and

(h) blocking means on said rotor member for preventing engagement of said locking means with said one member when the latter is axially spaced from said first position thereof.

4. In a machine as set forth in claim 3, said rotor member being radially aligned with said fan wheel means in said first position.

References Cited in the file of this patent UNITED STATES PATENTS Thomas Aug. 5, 1952 

